Available at: http://digitalcommons.calpoly.edu/theses/1071
Date of Award
MS in Engineering - Materials Engineering
CONSTRUCTING AND OPTIMIZING A SINGLE WAFER SOLAR CELL ARRAY IN THE MICROFABRICATION LAB AT CALIFORNIA POLYTECHNIC STATE UNIVERSITY AT SAN LUIS OBISPO
Solar cells are more and more becoming a significant source of energy in the world today. They are used to power entire buildings as well as small devices and everything in between, and are utilized all around the world. Smaller solar devices, such as hearing aid battery chargers, cost a lot of money relative to the monetary wealth in third-world countries. For this purpose, a less expensive, more efficient solar cell array should be developed.
This study contains research that details all aspects of how solar cells work. It also details three years’ worth of studies at California Polytechnic State University (Cal Poly) that attempt to fabricate a solar cell array on a single wafer.
Two tests were carried out that will help determine the optimal attributes of the solar cells. The first compared a solar cell made on a 10 µm thick silicon on insulator (SOI) wafer to solar cells made with the exact same masks on a 500 µm thick wafer. The thicker solar cell had 2.5 times the maximum power as the SOI solar cell. Aspects of the solar cell that would need to be improved are: increase thickness to between 70-100 µm from the SOI thickness, texture the front surface, add a passivation layer on the front surface, decrease the contact resistance for the metal electrodes, and add in a rear reflector. The next test was all about analyzing the metal contacts and interconnects. Ten gold-silver filled epoxy-gold bonds were constructed and measured ten times each, giving a grand mean between 10 and 11 Ω. Another short test was run with a commercial solar cell to characterize the change in power based on the series resistance. It was discovered that the both the epoxy and the gold add too much to the resistance. To fix this, a silver solder-like paste and a thicker contact metal should be used. There is also a derivation that details the design of a top contact layer that optimizes the finger spacing and finger width based on other solar cell factors. With the materials available at Cal Poly, a solar cell array can be fabricated on a single wafer. When accounting for the materials and processes available to the scientific community as a whole, a very effective and efficient solar cell can be fabricated.